Inerting fuel systems are widely used in airplanes where large amounts of fuel are stored. As fuel is consumed during a flight, the fuel level in the tank is lowered and the remaining oxygen in the tank is replaced by non-flammable inert gas (e.g., nitrogen enriched air) to prevent combustion. During flight, bleed air, which is compressed air taken from the compressor stage of the airplane's engine, is passed through air separation modules (e.g., molecular sieve beds) to produce the nitrogen enriched air. There is a continuing need to efficiently use the air separation modules.